Ever since 1950, when blood oxygenators made open heart surgery feasible, it has been possible to treat some forms of heart disease by replacing one of the patient's heart valves with a prosthetic valve. Early heart valve prostheses included ball-and-cage valves and disc-and-cage valves in which a ball or a disc was housed in a cage. One side of the cage provided an orifice through which blood flowed either into or out of the heart, depending on the valve being replaced. When blood flowed in a forward direction, the energy of the blood flow forced the ball or disc to the back of the cage allowing blood to flow through the valve. When blood attempted to flow in a reverse direction, or "regurgitate", the energy of the blood flow forced the ball or disc into the orifice in the valve and blocked the flow of blood.
A bi-leaflet valve comprised an annular valve body in which two opposed leaflet occluders were pivotally mounted. The occluders were typically substantially rigid, although some designs incorporated flexible leaflets, and moved between a closed position, in which the two leaflets were mated and blocked blood flow in the reverse direction, and an open position, in which the occluders were pivoted away from each other and did not block blood flow in the forward direction. The energy of blood flow caused the occluders to move between their open and closed positions.
A tri-leaflet valve comprised an annular valve body in which three flexible leaflets were mounted to a portion of the valve body, called a "stent," located at the circumference of the annulus. Some tri-leaflet valves used rigid leaflets. When blood flowed in the forward direction, the energy of the blood flow deflected the three leaflets away from the center of the annulus and allowed blood to flow through. When blood flowed in the reverse direction, the three leaflets engaged each other in a coaptive region, occluded the valve body annulus and prevented the flow of blood. The valve leaflets were made from tissue, such as specially treated porcine or bovine pericardial tissue or from a man-made material such as polyurethane or another biocompatible polymer.
A heart valve is implanted into an annular opening in a heart created when the diseased valve is removed. The valve can be secured in the annulus through the use of sutures or pins that penetrate the host tissue and an outside edge of the valve. Alternatively, a sewing ring can be attached, typically with sutures, to the elastic valve. The valve can then be secured in the annulus by suturing the host tissue to the sewing ring.
An important consideration in prosthetic heart valve design is the durability of the heart valve. Replacing a prosthetic heart valve after it has been implanted is dangerous and expensive for the patient and failure of a prosthetic heart valve can cause the death of a patient. One source of prosthetic heart valve failure is tearing of the elastic material that forms the heart valve.